The proposed research is to investigate the formation and behavior of chromosomal aberrations specifically tandem duplications, in bacteriophage, T4. The major areas of active investigation are: (1) Genetic mapping of duplication ends within an rII region. These data will allow a more critical assessment of the role of base sequence homology in the formation of duplications and correlated with segregation frequencies will provide an estimate of the size of the pairing region for recombination in phage T4. (2) Physical size and position of duplications, determined by electron microscopy of heteroduplex DNA. These data will be correlated with genetic mapping data and segregation data to better understand the mechanics of tandem $ duplications and the physical map of T4. (3) More stable duplications arise in stocks of Dp617-1 with a high frequency. These duplications will be analyzed to determine if they are derived from Dp617-1 by deleting material or if they are of independent origin.